BLOGS

On this happy anniversay–the 150th anniversary of the Origin of Species–let us contemplate one of evolution’s great works: the origin of giants.

Whales are the biggest animals to ever live. Blue whales can get up to 160 tons–about as heavy as 2000 grown men. They are trailed in the rankings by the fin whale and a few other related species of whales. There are no lobsters in their ranks, no clams, no rodents. All these giants feed in much the same way. They swallow up water and filter it through fronds in their mouths called baleen. Most of the food they eat is tiny stuff, like krill and other small invertebrates. So some scientists have wondered how big whales manage to put enough tiny bits of food in their bodies to get to such huge sizes.

Unfortunately, whales dine out of sight, so scientists have had to tackle those questions with indirect clues. Jeremy Goldbogen, a biologist now at the University of British Columbia, has gathered all the clues he can, from data recorders carried by diving fin whales to video of baleen whales feeding near the ocean surface. To make sense of that data, he has worked with zoologist Robert Shadwick and ad paleontologist Nick Pyenson, also of UBC, as well as Jean Potvin, a physicist whose speciality is parachutes.

Yes. Parachutes. Let me explain.

Potvin (left, with an accelerometer on his head) has been helping the biologists build a sophisticated physical model of a feeding fin whale. They set out to build a model that would produce the kinds of behavior that real whales do. For example, a fin whale will dive hundreds of feet down in search of food. Once it gets deep enough, it speeds up dramatically, and then abruptly slows down, almost stopping. Yet even as it slows, its tail is still moving up and down, generating tremendous thrust. Then, about half a minute later, it

speeds up and slows down again. What’s going on?

According to the scientists, this pattern occurs when the whales lunge into a cloud of krill and drop open their jaws. Pleats under the lower jaw open up, engulfing huge amounts of water. The whale slows down because of the drag. It behaves, in other words, a lot like a parachute.

I first wrote about this whale work two years ago for the New York Times when Goldbogen and his colleagues published some of their first results. Since then, Potvin has brought his expertise on parachute physics to these parachuting whales. He and the other scientists have developed a sophisticated new model that tracks the incoming water more carefully. It’s a lot of water, the scientists have found: in one lunge, a fin whale can momentarily double its weight.

If a whale simply let the water come rushing in, there would be a tremendous collision–more than a whale could handle. Instead, the scientists argue, the whales actively cradle their titanic gulp. As the water rushes in, the whales contract muscles in their lower jaw. The water slows down and then reverses direction, so that it’s moving with the whale. (It just so happens that fin whales do have sheets of muscle and pressure-sensinging nerve endings in their lower jaw. Before now, nobody quite knew before what they were for.) Once the water is moving forward inside the whale it can then close its mouth and give an extra squeeze to filter the water through its baleen.

This bizarre strategy may be the secret to the huge size of some whales. A fin whale can get 20 pounds of krill in a single gulp, but it can gulp every 30 seconds. Because krill live in gigantic swarms, they can keep gulping and get enough food in four hours to fuel their bodies for an entire day.

In order to make lunge-feeding work, you have to have a really big mouth to capture enough water in one gulp. But in order to have a big mouth, you need a big body. And in order to keep that big body running, you need to get a lot of food. And in the very act of getting that food–diving deep, lunging open-mouthed, and then pushing a school-bus-sized volume of water forwards–requires a lot of energy on its own.

Goldbogen and his colleagues wondered what sort of trade-off lunge-feeding whales faced between the costs and the benefits of eating like a parachute. To find out, they took advantage of measurements scientists made of hundreds of fin whales at whaling stations in the 1920s. Goldbogen punched the measurements into a computer and then analyzed the proportions of fin whale bodies of different sizes. From those calculations, the scientists also figured out how much water whales of different sizes could engulf.

It’s a general rule among living things that big organisms are not just magnified versions of little ones. The proportions of parts changes along the way. In some cases, these changes are the result of natural selection acting on different physical forces. For example, an elephant can’t stand on the delicate legs of a horse. They need legs shaped like stout pedestals to hold their bodies up against gravity. In other cases, the different proportions are just a result of development–some parts grow faster than others. This scaling exists not just between species, but within a single species. For example, a human pygmy is, in some ways, a scaled down version of a taller person. But their heads do not scale down the same way, because their brains are still about the same size as a taller person’s.

As they report today in the Proceedings of the Royal Society, Goldbogen and his colleagues found that big fin whales are not just scaled-up versions of little fin whales. Instead, as their bodies get bigger, their mouths get much bigger. Small fin whales can swallow up about 90% of their own body weight. Very big ones can gulp 160%. In other words, big fin whales need more and more energy to handle the bigger slugs of water they gulp. As their body increases in size, the energy their bodies demand rises faster than the extra energy they can get from their food.

This scaling may explain some of the weird diving patterns found in lunge-feeding whales. Blue whales are twice as big as humpback whales, for example, but both species dive for the same period of time (about eight minutes) and to the same depth (148 meters). All things being equal, you’d expect that blue whales would be able to dive deeper and longer, because they could store more oxygen in their bigger bodies. Blue whales also make fewer lunges than humpback whales (6 versus 15). It’s possible that the gigantic blue whales are hard up against a size limit. They need so much energy for their lunges that they can’t afford to hold their breath longer, and they can only manage to make a few lunges before they run out of reserves and have to head for the surface.

If the scientists are right, they may have discovered one of the big ironies in evolution. Lunge-feeding may have allowed whales to become the biggest animals ever to roam the planet. But this was not an open-ended invitation.r. Once whales got large enough, lunge feeding itself became so costly it prevented them from getting any bigger. Perhaps some day another animal will evolve a new strategy that will let it get even bigger than a blue whale. But for the animal kingdom as we know it, we may be sharing the planet with the biggest species it can offer.

Quick clarification: when you said blue whales can grow to be 160 tons, or about as heavy as 200 grown men, did you mean 2,000 grown men? If a ton is 2000 pounds, 160 tons is 320,000 pounds, which would equal 200 men of 1,600 pounds each! Whereas 2,000 grown men of a more reasonable 160 pounds would give you 320,000 pounds, or 160 tons.

[Carl: Thanks. I seem to have lost a zero along the way somewhere…Fixed.]

Is there a reason that bigger bodies can support much bigger mouths? The argument you make seems backwards:

“In other words, the bigger bodies need more and more energy to handle the bigger slugs of water.”

Seems like the advantage would be to stick with small bodies if big bodies require disproportionate amounts of energy.

I guess I should read the article.

[Carl: If you’re going to lunge-feed, big gulps mean more food. A very small whale may not get enough food from each gulp. But at big sizes, the cost of lunge-feeding may catch up, and then overtake, the benefits.]

Thanks Carl. Very informative. The idea of a size wall for blue whales is supported by the fact that no prehistoric animal, either plesiosaur or dinosaur, was as big as the blue whale, even though as reptiles they had an extraordinarily large amount of evolutionary space to “experiment” with super large body structures.

Now we have to keep the whales alive, and as important, the krill they eat, and the tiny critters the krill eat.

Omni Magazine ran a piece some years ago debunking a lot of popular science fiction ideas. One of the first to go were giant insects which the story claimed would not be able to support their own weight if scaled up to monster movie sizes.

[Carl: If you’re going to lunge-feed, big gulps mean more food. A very small whale may not get enough food from each gulp. But at big sizes, the cost of lunge-feeding may catch up, and then overtake, the benefits.]

Still not clear. Why would smaller bites in smaller whales be insufficient? The bioenergetic argument in the article would suggest that smaller whales could get more of their relative nutritive requirements in a single bite.

I’m guessing it’s another factor. Perhaps smaller whales can’t dive as deep to find the baleen, or something like that.

With regards to #3 and #9: The smaller mouths of the small whales are still large enough to catch the amount of food necessary to sustain the metabolism required by these bodies. The fact that their mouth are proportionally smaller (in comparison to those of fully-developed adults) may have something to do with growing up, from having to depend on mom’s milk at first to having to hunt for food later.

As for the size advantage: for marine mammals, bigger sizes are advantageous b/c they reduce heat loss (per unit mass). Its like the individual fingers in a glove vs. an entire hand in a mitten. Also for marine mammals, it turns out that bigness has helped in reducing the hydrodynamic drag of their bodies. Finally, with large animals being less maneuverable than smaller ones, the large size of the mouth turns out to help in defeating the escape strategies of the prey.

“Perhaps smaller whales can’t dive as deep to find the baleen, or something like that.” They are diving for plankton and small fish like herring, the baleen is what Zimmer describes here: “They swallow up water and filter it through fronds in their mouths called baleen”.

Carl, you say that as they get bigger animals are not usually scaled up versions of themselves, but that’s being a little simplistic. There’s a long running debate in animal morphology about exactly this notion, and, at least for mammals, the evidence seems to be that overall, larger species scale up isometrically relative to smaller species. That is, they’re mostly scaled up versions of smaller species. Of course, the relative proportions and shapes of body parts do vary a lot, due to natural selection as you say, but overall size and shape seem to scale “geometrically.” For instance, see Silva, “Allometric scaling of body length: Elastic or geometric similarity in mammalian design.” J. Mammology 79, 20-32 (1998).

And, this scaling holds for whales, too, for the most part. Actually, as whales get bigger, i.e., as we go from smaller species to larger species, they get bigger in all directions at basically the same rate, except that they do tend to get a longer slightly faster than they get wider, perhaps to reduce the drag on their enormous bodies.

If baleen whales could get that big only because they use lunge-feeding, what was the ichthyosaurs’ excuse? At 21 metres long and 60 tons, about as big as the average fin whale, Shonisaurus ties for second place in the all-time size stakes. But it had a skinny head, had a beak like a dolphin, and was shaped for speed like a dolphin. So it presumably chased down its prey like a dolphin too.

Pliosaurs only made it to 18 meters as far as we know, and were considerably skinnier (30 tons).

John, if I may jump in here, there are at least a couple of possibilities. One is that the prey Shonisaurus was hunting down individually was typically large and abundant, thus providing a sufficient amount of energy to sustain a large body size. Another is that Shonisaurus had lower metabolic needs than any living cetacean, since reptiles have lower metabolic rates than mammals, and thus needed less food to sustain a comparable mass.

To turn this question on its head, another way of asking it is to wonder why Shonisaurus wasn’t bigger than a Blue Whale. That is, if it could get so big without the benefits of baleen and lunge feeding, why not get bigger still by developing it? The answer to this is probably related to the evolutionary pressures that led to the development of baleen and lunge-feeding for some whales, but not for Shonisaurus and its cousins. It might also be a metabolic thing: baleen might require vast amounts of energy to maintain that Shonisaurus just couldn’t provide without fundamentally changing is cellular physiology (that is, increasing it’s metabolic rate).

Why can whales grow larger than other marine life? Does breathing air somehow enable (or encourage) you to get bigger?

[CZ: Well, squid, extinct marine reptiles, and some other animals do get fairly big. The biggest whales, however, are lunge feeders. That suggests that lunge feeding might make such big sizes possible. It’s a hypothesis that is now being tested with studies on fossils of whales.]

The big baleen whales pick their targets and engulf them with their giant jaws and extensible mouth/throat region. They are often feeding on swarms of krill that measure kilometers in extent. Rather than think of big whales as filter feeders, we should think of them as predators that take bites off of superorganisms that are hundreds of times larger. The fact that the krill are strained out of the water by the baleen is a matter of processing – it comes after the whale has taken a bite.

Interesting article, and interesting string of comments. This is my first time visiting this site, and I am impressed by the civility of the comments. I read a lot of political blogs and articles, and am always appalled by the rudeness of the people making comments. It seems that people have a hard time disagreeing without turning to name-calling, especially when there is no apparent consequence. Often the point of the article is lost while the commentators play tennis with insults.

While lunge feeders are large, and the blue whale is a lunge feeder, let’s not forget that the sperm whale is not a lunge feeder, and is larger than most lunge feeders. A blue whale weighs up to 200 tons, but the fin whale is the second largest whale, and only weighs up to 65 tons. A sperm whale is similar in length and weight to a fin whale, an larger than most other lunge feeders. Lunge feeding does not seem like the only path. It has advantages, I am sure. By eating plankton, they have less concern about finding prey or prey escaping, for example. But big can come from other directions.